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MP: peer shakiness ROOT-CAUSED as single-box packet jitter (rig, not game) + affinity launcher (task #50)

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The residual RANDOM peer shakiness on accel/decel was proven (BT_RXJIT record
inter-arrival probe) to be TEST-RIG packet jitter, not the game: two Debug btl4
nodes on one box contend for CPU, so Windows batches their TCP delivery -- records
arrive in bursts (max 56-226ms gaps, burstiness 3-7x) instead of even ~17ms.  The
peer dead-reckons across the gaps then snaps -> random shake.  Pinning the nodes to
disjoint cores restored even ~17ms delivery (burstiness ~1.0) and the shakiness
vanished (user-confirmed 'that was it').  Real pods = dedicated machines, no
contention -> never see it.  So NO un-authentic jitter buffer -- the coupled
body-channel peer (96a896a/f094d78/23f1532) is the authentic + correct finish.

 - mech.cpp: BT_RXJIT record-arrival-jitter probe (env-gated).
 - tools/mp_launch.sh: 2-node launcher that pins nodes to disjoint cores (bakes in
   the fair-delivery condition; documents why).
 - context/multiplayer.md: the finding, so it is not re-litigated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
arcattack
2026-07-15 08:14:22 -05:00
co-authored by Claude Opus 4.8
parent 23f1532fb0
commit 49d73dc8e2
3 changed files with 69 additions and 0 deletions
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@@ -405,3 +405,7 @@ Decomp-verified (workflows w0odszxro/wh1h5gnmc, 3 make-or-break claims adversari
- T4 CLOSED: both leg(0x65c) and body(0x6bc) animators are AnimationInstances of the SAME JointedMover/JointSubsystem (JMOVER.cpp:1382) -- either poses the WHOLE skeleton. Our port keeps the peer on the LEG channel (body unbound on the peer); faithful functional equivalent.
RECONSTRUCTION STATE: coupled path is DEFAULT ON (mech4.cpp: s_drPos gait-coupled, s_gaitMirror/Send). Reverts: BT_DR_POS=1 (peer velocity), BT_NO_MASTER_GAITMIRROR (master const-vel mirror). Measured: single-source coupling backward-steps 0.1% (vs the two-source split's churn), position ratio 1.043. RESIDUAL (follow-up): occasional ~2.9u snap from the leg(peer)-vs-body(mirror) channel mismatch -- to close, run the master mirror on a leg-channel prediction fed last-sent speed, matching the peer's poser. Also open: exact _DAT_004ab9cc decay constant; whether IntegrateMotion's 2-stage angular integrate is intended.
## Peer motion: the "random shakiness" is single-box packet jitter, NOT the game (task #50, 2026-07-15) [T2]
After the coupled body-channel peer landed (96a896a + turn-step f094d78 + cadence-mirror 23f1532), residual peer shakiness on accel/decel was RANDOM -- sometimes perfect, sometimes shaky. Root cause is the TEST RIG, proven with BT_RXJIT (record inter-arrival ms on the peer): two Debug btl4 nodes on ONE box contend for CPU, so Windows BATCHES their TCP delivery -- update records arrive in bursts (min ~0ms back-to-back, max 56-226ms gaps, burstiness max/avg 3-7x) instead of an even ~17ms. A peer dead-reckons across the long gaps then snaps when a record lands -> random shake. Pinning each node to a DISJOINT core set (ProcessorAffinity 0x00F / 0x3C0) restored even ~17ms delivery (burstiness ~1.0) and the shakiness vanished (user-confirmed). REAL pods are dedicated machines with no contention -- they never see this. DO NOT add an interpolation/jitter buffer or other un-authentic netcode to mask a single-box artifact. Use tools/mp_launch.sh (bakes in the affinity) for all 2-node tests. Diagnostic env: BT_RXJIT (arrival jitter), BT_SLIDE ([slide]/[mslide] slide-in-stand), BT_GAITEV, BT_MIRDIV, BT_NO_MIRROR_CAD / BT_PEER_LEGCH (revert the coupled-peer fixes).